Multiple horizon oil production method



Oct. 23, 1956 R. sPEARow 2,767,792

MULTIPLE HORIZON OIL PRODUCTION METHOD Filed June l0L 1955 2 Sheets-Sheet l l INVENTOR. R040@ Sped/vw BY mf R. SPEAROW MULTIPLE HORIZON OIL PRODUCTION METHOD oct. 23,1956

Filed June 10, 1953 INVENToR. Ha/7 pea/"0W BY fn@ A'TORNEL/ United States Patent 2,767,792 MULTIPLE HORIZON OIL PRODUCTION METHOD Ralph Spearow, Paola, Kans.

Application June 10, 1953, Serial No. 360,645

Z Claims. (Cl. 166-10) This invention relates to a method of producing oil wells having in a single well one or more producing horizons and refers more particularly to such a method wherein gaseous pressure is applied to the top portions of the horizons to be produced and oil is removed from the lower portions of ysaid horizons. This method is designed to be employed either in newly drilled well locations or in secondary recovery production.

This application is a continuation-in-part of my copending application Serial No. 262,568, tiled December 20, 1951, now Patent No. 2,725,106, which in turn is a continua-tion-in-part of my earlier applica-tion Serial No. 750,396, filed May 26, 1947, and issued on April 22, 1952, as Patent No. 2,593,497.

The present method represents an adaptation of the gas pressurization oil production techniques set forth in my previous applications to permit their employment in new wells or secondary recovery situations where the well to be produced has had its sands shot with explosives, thus forming large caverns within the sands at the bottom of the borehole and in wells where it is desired to produce more than one oil horizon in a single well.

One of the distinctive features of my oil production methods as set forth in this and my previous applications is that gaseous pressure is applied to the -top portions o-f the oil horizons and oil is produced from the lower portions of said horizons, the oil within the horizon being driven vertically downward by the pressurization, Such gas pressurization methods are feasible and workable only when the casings of the wells employed are properly sealed throughout portions of their lengths in, as well as above and below, the horizons to be produced.

For example, if separate pressure and production wells are employed in such a method, it is necessary for the production well casing to be sealed to the borehole wall from a point above the top of the oil horizon through the horizon to the oil intake zone on the production casing. Furthermore, it is necessary to seal the casing of the pressure well to the well wall at the top of the oil horizon. If the pressure well is not so sealed, the gaseous pressurizing agent may escape into the formations above the oil horizon, and pressure thus be lost and, if the production well is not so sealed, the pressurizing agent will diffuse along the top of the oil horizon until it reaches the production well and then pass down the outside of the unsealed production casing and escape through the oil intake holes in the production casing without producing oil or serving as a pressurizing agent.

Similar considerations apply when a single well is used both for pressurization and production, but will not be detailed here as the present invention employs separate pres-sure and production wells.

The advantages of a successful gaseous pressurization method lie in the very high percentage of oil recovery from the sand and the minimal expense as compared with other pressurizing methods such as water drive.

A tremendous advantage of the Spearow gas pressurization methods, which involve sealing the casings 'of the' pressure and production wells to the surrounding formations to permit no escape of pressure from the horizon except at the oil withdrawal points, is the fact that when the pressurization of the horizon has proceeded to a certain level it is possible to shut down the compressors and continue to produce oil by the agency of sealed-in pressures for a long-time interval without further input of pressure into the horizon. This result is greatly in contrast to a pressurization method such as water drive, wherein shutting down of the water pumps causes the production of oil, by water drive means, to cease immediately. As an example of this performance of the Spearow method, in an actual operation in Eastern Kansas the compressors to a field of over twenty wells producing under gaseous pressurization werey shut off for a period of over ve weeks and at the 'end of this time (the present Writing) the wells were'still flow-ing and pumping oil without any diminishing in volume. This is addi-tional proof of the necessity of sealing the space between the casing and the formations and the effectiveness of that sealing.

Previously, attempts have beenmade to produce oil wells by introduction of gaseous pressure into the horizon and moving the oil horizontally through the sand. Attempts have also been made where the presure was introduced into the horizon above the desired oil withdrawal zone. None of these methods has proved practical because the practice of properly sealing the pressure and production casings to the earth formations Within the Well as delineated above was not conceived and employed. Many wells which are desired to be produced in secondary production were perforated or shot to increase production. The result of shooting an oil horiz-on within a well is the formation of a relatively large shot hole cavern in the horizon surrounding the borehole of the well. This cavern poses a severe problem if it is desired to properly seal a production casing within the originall borehole and practice a secondary recovery method utilizing gaseous pressurization. Similarly, under certain permeability conditions, it is often desirable to Shoo-t the oil horizons in newly drilled wells.

Furthermore, many well locations have access to more than one oil horizon in a single borehole and it is advantageous to produce these multiple horizons from the single hole. Such a situation may occur in original or secondary production and in either the horizons may or may not have been previously shot. It is therefore highly desirable that a method of producing such well-s be provided utilizing gaseous pressurization with its concomitant advantages. I

Therefore, an object of the present invention is` to provide a method of producing oil from more than a single horizon within a single well, by applying gaseous pressure to the top portions of the horizon-s, irrespective of whether the horizons have been shot previously.

Another object of the invention is to provide a method of producing wells having perforated oil horizons by applying gaseous pressure to the top portions of the horizons and withdrawing oil from the lower portions of the horizons.

Another object of the invention is to provide a method of producing oil wells by applying gaseous pressure to the top portions of the horizons and withdrawing oil from the lower portions of the horizons wherein the pressurization may be applied intermittently to the horizon with the production remaining relatively independent of the pressurization periods. p

A further object is to provide a method of producing wells containing more than a single producing horizonv and wells containing shot caverns in the producing horizons in which pressure is applied to the top portions of the oil horizons through pressure wells whose casings are sealed to the well wall at the cap rock of the respective arested oct. 23, sl

horzosand in which oil is produced from production above the cap rock of the producing horizons through the horizons to the oil intake holes in the production casings.

Other and'further objects will appear in'thc'ors'e of the following description:

Fig: 1 is a cross-sectional view taken through' tlieg logic structure of an oil' field showingtwo wells, o'n'e of which is a pressure well, the other a production welllv Fig; 2 is a' cross-sectional view taken through the geologic structure of an oil field showing three wells, one apressure well, the others production wells.

In the description like reference numerals will be used toindicate likepart's in thevarious views.A I

Referring to the drawings, Fig. 1 will b first described as it illustrates the' method as performedin a single 'oil-producing sand.

The groundlevel is indicated at` Oil horizon 11 has a relatively impervious cap 12 which is topped by earth formations'l. Borehole 14 extends through oil horizon llland`has a shot hole cavern 1S. Positioned within bo'rel'iol'e'14 and extending to the'vicinity of the bottom of horizon 11 is production casing 16 having perforations 17 near its lower end. A pumpingstring nipple 18 is shown inside the casing 16 and fastened to the outside of casing 16`above perforations 17 is baie collar 19. Surrounding casing 16 in the vicinity of the perforations 17 is placed a batch of'pea gravel 20. On top of gravel 20V is placed a layer of granular insulating material 4such as sand. Production casing 16 has a cement seal 22 to the well wall from a point above the top of horizon 11 to the sand layer 21. Withdrawal pipe 23 is connected into casing 16 above ground level 10.

At 24 in Fig..l is shown the borehole of a pressurization well which is drilled into the top of horizon 11.- Pressure casing 25 having-perforations 26 near its lower end, extends into the top of horizon 11. Casing 25 is likewise sealed as shown at -27 from the top of horizon 11 to any desired point above horizon 11 `according to thecharacter' of the formation. above the surface into casing 2S.

In Fig. 2 is shown the method as applied to wells reaching multiple production horizons, illustrating' an Unperforated well and a well having-shot cavernsin the-producing horizons.

Referring first to theV production well at the right side of the gure where the caverns appear-,f groundlevel-is again designatedas 10. The upper oil horizon 11a and lower' oil horizon 11b have impervious caps 12 topped by earthformations 13.` Borehole 14a extends through-bili horizons 11a and 11b, both of which have shot Caverns Positioned within boreholel 15a and 15b respectively. 14a and extending-to the -vicinity of the bottom-of horizon 11a is primary production casing 16a having' perforations l'lafnearits lower end. Surrounding casing -16a in the vicinity of the perforations 17a is` placed a'batch of'pea" gravel 20a and above the gravel is placed a layer of sand or other insulating material 21a. Productionf'casingla is likewise sealed by a column 22a ofcernenttto' the well wall `from a point above-theftop of' horizon lla'to the sand layerv21a, the locationtof4 the top Vof'vthe` cement column being governed by the character of the forma'- tions labove the oil sand; Withdrawal pipe 23a is connected-into casing 16a above ground level 10: Positioned" within primary production casing 16a and extending to'the vicinity of the bottom of horizon'llb 'is` secondary pro-v duction casing or tubing 16b havingperforations 17b near its lower end. A pumping string nipple 18b is'sho'wnI inside the casing 16b and fastened to the outside ofI casing 16h above perforations 17Hl isbafe collar' 19]). Surrounding casing 16]) in they vicinity oftperforations 17b is placed a bed of pea gravel 20b`. Orithe'top 'offr gravel 20h isv alayerof sandI or other insulating material` 2lb." Productioncasing 16bhas` 'a' seal 2217' tth'e'well Pressure input pipe 28 is connectedwall from the top of sand layer 2lb to the vicinity of the bottoni ofvcas'ingla. Oil' withdrawalV pipe 23b is connected to casing 16b above ground level 10. Pumping string 29a is shown within the annulus between production casings 16a and 16b extending from the ground level to the vicinity of perforations 17a in casing 16a.

Referring now to the production well in the center of Fig. 2 without shot Caverns, borehole 14e extends through oil' horizons 11a` and 11b; Positioned within borehole 14e and extending to the vicinity of the bottom of horizon 11a is primary production casing 16e` having perforations 17C nearits lower end. Production casing-16e is sealed as shown at 22C to the well wall from a point above the top of horizon 11a tothebottomiof'casing 16c according to the character of the formation. Casing 16e and its surrounding annular seal are perforated near the bottom of horizon 11a. Withdrawal pipe 23e is connected to casingltc above the ground level 10. Positioned within` casing'lc and extending to' the vicinity of the bottom of horizon 11b is secondary production casing 16d;

Pumping string nipple 18d is shown inside casing 16d. Secondary production casing ld'has aseal' 22d` to the well wall from aV point adjacent the bottom ofprimary production casing 16'c to the bottom of secondary production casing 16e. Secondary production casing 16d` and its surroundingfannular seal 22d are perforated near the `bottom of oil'horizon 11b. Oil withdrawal pipe 23d is connected to casingld above ground level 10. Positioned within the annulus be't'weenproduction casing's 16C and 16d is pumping string'29c extending from ground level" to the vicinity of the perforations in casing 16 and its` surrounding annular seal.

At 24a in Fig. 2 is shown the' `borehole of a pressurization well -which is drilled throughl horizon lla'into the top of horizon 11b. Pressure casing"25a extends into thetop of horizon 11al and has a seal 27a` from the top of horizon 11a to any desired point above horizon 11a4 ing 25a. Pressure input pipe`28bis connected into 'casing 25h. At 30`is shown a conventional'packer set on'casing`4 24b to forma bond between itI and the holebore of `thepressurization well.

Referring first to the"operatin "-of the method ina single oil horizon as exemplified-in'Fig. '1, acasing 16` perforated'ne'ar its lower end is -run intothe borehol`e14 of a well and tothe vicinity ofthe bottom of the oil horizon 11. The casingis then gravel packed in theyicinity of the perfo'ations 17. The material used issuitable granular material such assmoothand normally round,'clean; pea" gravel 20. Probably the best size is" gravel 1A to 1/5 of Thi'sgravel actsr a's` a' suitable aninch-in diameter. screen through which the:oil"rnay'enter the casi'ng"fr`om the sand'bodyand functions" as 'abse uponwhich it is possible to'securely seal offthe upper portions of the oil sand in the shot hole 14 through the oil sand. A layer of sand or other insulating .material 21 is next placed on top=of the gravel. The -material best employed here is common builders sand; This layerof `sand or' other similar material will suiciently separate and insulate the gravel `bed fromthe cementorbth'er 'sealing material 22. The Vborehole 14 surrounding'thfcasing is` then sealed from the top of 'thesndflayer'to a level above the top of the oil horizon. If desired;4 this material may extend'to the vicinity; ofthe"l ground' level. It is very important that'this cementor sealingrnate'rial bo'ndivith theioil'satllr'ted Wall'of'the oil horizon and thus proventi any marginal migration lof 4the pres'su're Aagent or sand iluids"`d`wnwardbetween it and the-oil sand once the` pressure agent comes in contact as it must, with the sealed shot hole.

Gaseous pressure is then applied to the top portions of the oil horizon to cause the fluid oil to migrate downwardly within the oil horizon and flow through the perforations in the casing. To accomplish this, a pressure well 24 is drilled to the top of the -oil horizon 11 as shown. A casing 25 is run in the pressure well and sealed to the earth formation from the top of the oil horizon to a point above the top of the oil horizon. If desired, this seal 27 may be extended to the vicinity of the ground level. All casing seals in both pressure and production wells must be of sufficient strength to secure whatever pressures are employed in driving the fluid and gaseous hydrocarbons downward through the sand body and must offer no means of escape for these pressures except at the points designated at the base of the oil sand. The method as above described can be employed with a plurality of production wells or a plurality of pressure and production wells. Furthermore, when desired, pumping strings may be employed within the production casings to aid in the recovery of the oil from the horizon when the pressures are not sufficient to raise the oil to ground level.

Referring now to the method as practiced in 4a production well of the type illustrated at the right side of Fig. 2, a primary production casing 16a perforated near its lower end is run within the borehole 14a of the well to the vicinity of the bottom of the upper oil horizon 11a. The primary production casing is then gravel packed in the vicinity of the perforations 17a. A layer of sand or other insulating material 21a is next placed on top of the gravel 20a. The borehole 14a surrounding the primary production casing is then sealed from the top of the sand layer to any desired level above the upper oil horizon. A secondary production casing 1Gb perforated near its lower end is run within the primary production casing 16a to the vicinity of the bottom of the lower oil horizon 11b. The secondary production casing is then gravel packed in the vicinity of the perforations 17h. A layer of sand 2lb is placed on top of the gravel 20h. The borehole 14a surrounding the secondary production casing is then sealed from the top of the sand or other insulating material to a point adjacent the lower end of the primary production casing. Pressure is then applied to the upper portions of the upper and lower oil horizons to cause the oil to migrate downwardly and flow through the perforations in the respective production casings. As the method of applying pressure to the multiple horizons is similar for both embodiments of the method illustrated in Fig. 2, detailed description lof the pressure well will be omitted until completion of the description of the production Well illustrated 4in the central portion of Fig. 2.

Referring now to the production well illustrated in the central portion of Fig. 2, a primary production casing 16C extending to the Vicinity of the bottom of the upper oil horizon 11a is sealed through the upper oil horizon from a point near its bottom to a point above its top. This seal 22e may be extended to the vicinity of the ground level if desired. The primary production casing and its surrounding seal are then perforated near the bottom of the upper oil horizon. A secondary production casing 16d is positioned within the primary production casing extending to the vicinity of the bottom of the next lower oil horizon 11b. The secondary production casing is sealed through the lower oil horizon from a point near its bottom to a point adjacent the lower end of the primary production casing. The secondary productioncasing and its surrounding seal 22d are perforated near the bottom of the lower oil horizon. Pressure is then applied to the upper portions of the upper and lower oil horizons whereby the oil migrates downwardly and flows through the perforations in the production casings 16C and 16d.

Pressure is applied to the upper portions ofthe upper and lower oil horizons through a pressure well 24a drilled through the upper oil horizon and into the top of the lowest oil horizon. A primary pressure casing 25a is run into the top of the upper oil horizon and sealed from the top -of the upper oil horizon to any desired point above the top of the said horizon. A secondary pressure casing 25b is run within the primary pressure casing into the top of the lower oil horizon and sealed from the top of the lower horizon to a point adjacent to but below the lower end of the primary pressure casing. A conventional packer 30 is ordinarily set on the secondary casing to bond between the casing and the'holebore. The packer keeps a full pressure seal at the top of the lower horizon. The packer is set at this point rather than reduce the size of the hole enterling the oil sand. The packer can be eliminated by seating the casing 2511 on the top of the horizon but the holebore 24a then entering the lower oil sand would be reduced to the internal diameter of the casing. This wouldrestrict the intake wall area for introduction of pressure and might not be feasible if the permeability factor in the oil sand is low. The considerations set forth in the description of the method as applied in Fig. l relating to the seals between the casings and the well walls apply with equal force in the multiple horizon application of the method. i Pressure is applied to the upper portions of the upper and lower oil horizons through the primary and secondary casings and oil is withdrawn from the bottom portions of said horizons through the perforations in the primary and secondary production casings. If the formation pressure is insufficient to lift the oil to the surface, pumping strings may be inserted in the primary and secondary production casings to assist in the removal of oil from vthe horizons.

As noted earlier in the specification, once pressurization -of a horizon has proceeded to successful production from the horizon, it is feasible to intermittently shut down the compressors and continue to produce oil by the agency of sealed in pressures for long time intervals. This performance is, of course, feasible only when the pressurization and production wells are sealed properly as delineated above.

If it is desired to apply the method to wells having more than two producing horizons, additional production casings may be run within the primary and secondary production casings and gravel packed or sealed to through the lower oil horizon in the same manner as described above, depending on whether or not the horizon has been shot or not. Similarly, the pressure wells may be extended to additional horizons.

A method of producing oil Wells by gaseous pressure applied to the top portions of the horizons to be produced where oil is removed from the lower portions of said horizons has thus been provided applicable to wells having one or more producing horizons and also applicable to wells with either perforated or unperforated oil sands. This method is made practical by provision of techniques of sealing the well walls to the surrounding producing and the nonproducing horizons.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the structure.

lt will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of thev invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, I claim:

1. A method of producing an oil well having a plurality of producing horizons comprising the steps ol positioning and sealing a primary production casing to the upper oil horizon to be produced from a level near the bottom of said upper oil horizon to a level above the top of said upperoil horizon, perforating the primary production casing and its surrounding seal near the bottom of said upper oil horizon, positioning a secondary production casing within the primary production casing and sealing it to the next lower oil horizon to be produced from a level near the bottom of said next lower horizon to a level adjacent the lower end of the primary production casing, perforating the secondary production casing and its surrounding seal near the bottom of the next lower oil horizon to be produced, and applying iiuid under pressure to the upper portions of the oil horizons desired to be produced whereby the oil within said horizons is caused to migrate downwardly and iiow through the perforations in the respective production casings.

2. A method as in claim 1 applied in a plurality of production wells.

3. A method as in claim 1 wherein oil is pumped from the production casings,

4. A method as in claim l wherein the pressure is applied intermittently to the upper portions of the horizons.

5. A method of producing an oil well having a plurality of producing horizons comprising the steps of positioning and sealing a primary production casing to the upper oil horizon to be produced from a level near the bottom of said upper oil horizon to a level above the top of said upper oil horizon, perforating the primary production casing and its surrounding seal near the bottom of said upper oil horizon, positioning a secondary production casing within the primary production casing and sealing it to the next lower oil horizon to be produced from a level near the bottom of said next lower horizon to a level adjacent the lower end of the primary production casing, perforating the secondary production casing and its surrounding seal near the bottom of the next lower oil' horizon to be produced, drilling a pressure well into the top of the lowest oil horizon desired to be produced, running-primary pressure casing into the top of said upper oil horizon to be produced, sealing said primary pressure casing from the top of said upper oil horizon to a level above the top of said upper oil horizon, running a secondary pressure casing within the primary pressure casing into the top of the next lowest oil horizon to be produced, sealing said' secondary pressure casing from the top of said next lower oil horizon to a level adjacent to but below the lower end of the primary pressure casing, applying iiuid under pressure to the upper portions of the oil horizons tol be produced through said' pressure casings whereby the oil within said horizons is caused to migrate downwardly and flow through the perforations in the respective production casings and recovering the oil from said production casings.

6; A method as in claim 5 applied in a plurality of pressure and production wells.

7. A method of producing an oil well with a shot cavern in the horizon portion of the borehole comprising the steps of running a casing perforated near its lower end into the borehole of th'e well and to the vicinity of the bottom of the oil horizon to be produced, gravel packing the casing in the vicinity of the perforations, placing a layer of line, granular material on top of the gravel, said fine granular material being of finer texture and lesser diameter than said gravel, sealing the borehole surroundingthe casingfrom the top of'the tine, granular layer to a level above the topof the oil horizon, and apply' ing Huid under pressure to the top' portion of the oil hori-v zon :to cause the oil to migrate downwardly and` ow: through the perforationsin thecasing.

S. A method as in claim 7 applied in a plurality of production wells.

9. A method as in claim 7 wherein oil is pumped from the production casing.

10. A method as in claim 7 wherein the pressure 1s applied intermittently to the upper portions of the horizons.

l1. A method of producing an oil well with a shot cavern in the horizon portion of the borehole comprising the steps of running a production casing perforated near its tower end into the borehole of the well and to the vicinity of the bottom of the oil horizon to be produced, gravel packing the production casing in the vicinity of the perforations, placing a layer of tine, granular material on top of the gravel, said tine, granular material being of finer te: irc and lesser diameter than said gravel, sealing the borel. le surrounding the production casing from the top of the tine, granular layer to a level above the top of the oil horizon, drilling a pressurization well to the top of the oil horizon to be produced, running a casing in said pressurization well and sealing it to the earth formations from the top of the oil horizon to be produced to a point above the top of said oil horizon, applying uid under pressure to the upper portion of said oil horizon through the pressurization well whereby the oil migrates downwardly and il'ows through perforations in the production casing.

12. A method as in claim l1 applied in a plurality of pressurization and production wells.

13. A method of producing an oil well having multiple oil horizons within the well and shot Caverns in the horizons comprising the steps of running a primary production casing perforated near its lower end within the borehole of the well to the vicinity of the bottom of the upper oil'horizon, gravel packing the primary production casing in th'e vicinity of the perforations, placing a layer of line, granular material on top of the gravel, said tine, granular material having" a finer texture and lesser diameter than said gravel, seaiing the borehole surrounding the primary production casing from the top of the fine, granular layer to a level above the upper oil horizon to be produced, then running a secondary production casing perforated near its lower end within said primary production casing to the vicinity of the bottom of the lower oil horizon to oe produced, gravel packing the secondary production casing in` the vicinity of the perforations, placing a layer of tine, granular material on top of the gravel similar to that relative the Iirst production casing, sealing the borehole surrounding the secondary production casing from the top of the tine, granular layer to a point adjacent the lower end of the primary production casing, and applying r'iuid under pressure to the upper portions of the upper and lower oil horizons to be produced to cause the oil to migrate downwardly and tiow through the perforations in the respective production casings.

14'. A method as in claim 13 applied in a plurality of production wells.

15. A method as in claim 13 wherein oil is pumped from the production'casings.

16. A method as in claim 13 wherein the pressure is applied intermittently to the upper portions of the horizons.

17. A method of reconditioning and producing an oil well having-multiple oil horizons within the well and shot Caverns within the horizons comprising the `steps of running a primary production casing perforated near its lower end within the borehole of the well to the vicinity of the bottom of the upper oil horizon to be produced, gravel packing the primary production casing in the vicinity of the perforatio'ns, placing a layer of fine, granular material o`n` top of thev gravel., said tine, granular material having a finer texture and lesser diameter than the gravel, scaling the borehole surrounding the primary production casing lfrom the top of the line, granular layer to a level above the top of said upper oil horizon, running a second-` ary production casing perforated near its lower end within the primary production casing to the vicinity of the bottom of the lower oil horizon to be produced, gravel packing the secondary production casing in the vicinity of the perforations, placing a layer of line, granular material on top of the gravel, said fine, granular material of the same character as that positioned relative the primary production casing, sealing the borehole surrounding the secondary production casing from the top of the line, granular layer to a point adjacent the lower end of the primary production casing, drilling a pressurization well into the top of said lower oil horizon, running a primary pressurization casing into the top of said upper oil horizon, sealing said primary casing from the top of said upper oil horizon to a point above the top of said upper oil horizon, running a secondary pressurization casing into the top of said lower oil horizon, sealing said secondary pressurization casing from the top of said lower oil horizon to a point adjacent to but below the lower end of the primary pressurization casing, applying uid under pressure through the primary and secondary pressurization casings to the tops of said upper and lower oil horizons, accumulating and producing oil from the production wells.

18. A method as in claim 17 applied in a plurality of pressurization and production wells.

19. A method of producing an oil well having a plurality of producing horizons comprising the steps of positioning and sealing a primary production casing within the well bore opposite the upper oil horizon to be produced from a level near the bottom of said upper oil horizon to a level above the top of said upper oil horizon, said primary casing having an inlet opening adjacent the lower end thereof thereby providing uid communication from the lower portion of said upper oil horizon into the lower part of the primary production casing, then positioning and sealing a secondary production casing positioned within the primary production casing to the next lower oil horizon to be produced from a level near y the bottom of said next lower horizon to a level adjacent the lower end of the primary production casing, said secondary casing having an inlet opening adjacent its lower end thereof thereby providing access from the lower portion of the lower oil horizon into the lower part of the secondary production casing and applying pressure to the upper portions of the oil horizons desired to be produced whereby the oil within said horizons is caused to migrate downwardly and flow into the respective production casings.

20. A method as in claim 19 wherein the pressure is applied intermittently to the upper portions of the Vhorizons.

References Cited in the le of this patent UNITED STATES PATENTS 1,252,557 Dunn Jan. 8, 1918 1,816,260 Lee July 28, 1931 2,107,006 Lang Feb. 1, 1938 2,277,380 Yancey Mar. 24, 1942 2,325,218 Beissenger July 27, 1943 2,368,428 Saurenman Ian. 30, 1945 2,403,987 Lewis July 16, 1946 2,593,497 Spearow Apr. 22, 1952 2,665,759 Childers Jan. 12, 1954 

